(A) Field of the Invention
This invention concerns ceramic fibers and more particularly concerns refractory fibers commonly used for insulating high temperature furnaces.
(B) History of the Prior Art
In the prior art, refractory fibers containing alumina were used as insulation in high temperature applications especially in high temperature furnaces. Such prior art fibers which were flexible enough to be easily applied to a furnace wall had a serious disadvantage since after being applied to a furnace wall, they tended to shrink at temperatures as low as about 1000.degree. C. and would seriously shrink, e.g., as much as 5%, at temperatures of about 1250.degree. C. Shrinkage of such prior art fibers or mats and blankets made from such fibers became totally unacceptable at temperatures in excess of 1250.degree. C.
Fibers or mats and blankets made from refractory fibers which did not shrink at unacceptable levels at temperatures in excess of 1250.degree. C. were too brittle to permit such fibers, mats or blankets to be easily installed as insulation within a furnace.
Examples of materials which have insufficient flexibility for ease of installation are disclosed in U.S. Pat. No. 3,935,060 to Blome et al, U.S. Pat. No. 3,865,599 and U.S. Pat. No. 3,982,955 to Mansmann et al.
An example of a refractory fibrous material which has sufficient flexibility to be installed into a high temperature furnace is disclosed in British Pat. No. 1,481,133 assigned to The Babcock and Wilcox Co. and published July 27, 1977 subsequent to the making of the invention disclosed herein. This material does not, however, have sufficient shrink resistance to make it desirable for use at temperatures above 1250.degree. C.
In areas unrelated to fibers, other prior art information is available concerning solid refractory substances which are pre-heated prior to use. Among such prior art are U.S. Pat. Nos. 1,807,915; 2,102,976; 2,524,601; 3,754,950; 3,826,813; 3,857,923; 3,880,971 and 3,903,225.